In a pattern forming technology, manufacturing of semiconductor devices using photolithography is in practice. The photolithography is a method of forming a desired pattern on a reticle being a photomask and transferring the pattern on a sample substrate via a reduction optical system. Photosensitive resin called a resist is formed on the sample substrate, and making use of a difference, between an exposed portion and an unexposed portion, in dissolving rate in a developing solution, a latent image of the transferred pattern is developed to form a pattern, and then etching follows, so that a material can be processed as desired.
In an exposure technology, in order to precisely transfer a microscopic pattern, the influence of proximate patterns is calculated and determined for correction, in addition to optimizing the wavelength of exposure light and a reticle structure. This correction is called OPC (Optical Proximity Correction), and a correction amount of a transferred image of the pattern is calculated based on the influence of an optical proximity effect obtained by calculation or by an experiment, considering lighting conditions (NA, Sigma), exposure conditions (a material of the resist, exposure wavelength) and so on of a stepper, thereby correcting the reticle size.
However, there is a factor uncorrectable by OPC, for example, size difference in scarce and dense patterns that is caused by flare of the stepper or at the time of etching, and the size of the formed patterns varies. The flare of the stepper is generated by minute irregularities of a lens or variation in refractive index of a lens, or by reflected and scattered light on a wafer surface. Further, local occurrence of flare depending on the condition of a surrounding area of each pattern has recently been recognized as a problem. This is a so-called local flare, and it is caused by peculiarity of a material of the lens depending on the wavelength (short wavelength of, typically, 193 nm) of the exposure light used and is a major factor of causing an unexpected change in shape and line width of the transferred pattern. Further, in etching, a region having a large etched area runs short of reaction gas or has increased reactive products, which causes precision deterioration of pattern formation depending on the area or the size in some region.
However, precise correction of such size variation caused by the local flare of the stepper and the loading effect in etching is difficult.
The above-described local flare should be quantified and eliminated in order to accurately form desired patterns in a semiconductor device, but this is a problem which has drawn attention just recently as described above, and therefore, currently no suitable technique of intentionally solving this specific problem of the local flare has been devised.
Further, in the optical proximity effect correction, the optical proximity effect is calculated based on patterns in a region within several μm, but time restriction makes it difficult to widen a calculation range to several ten μm as is required for the calculation of the influence of the flare, and it has been difficult to explain the influence of flare by the proximity effect of light intensity. Moreover, the influence of the loading effect in etching, as a matter of course, cannot be accounted for by optical intensity calculation.
The present invention was devised to solve the above-described problems, and an object of the present invention is to provide a pattern size correcting device and a pattern size correcting method that enable quantitative estimation of size variation occurring in patterns exposed in lithography and easy and accurate correction of pattern size based on this estimation, thereby enabling production of an extremely reliable device.